Agricultural and Utility Barns vs. Residential Barns: What Makes Them Different?

What’s the difference between a barn with a hayloft and a barn with a loft apartment? If you build an agricultural barn with a future living space in mind, can you convert it later and save money? Is it more affordable, or even legal to convert an existing agricultural barn on your property to a residential space? Why do barn apartments cost more than standard agricultural or utility barns? These are all questions you’re likely to come across if you’re researching barn or barn apartment projects.

Barn Pros specializes in both agricultural (ag) barns, utility barns and residential (res) barns, and in this article we’ll speak to how these structure classifications differ, and how they affect your permitting needs, project costs and timelines.

Understanding risk catagories

When considering structures classified as ag/ utility, or res, it’s crucial to understand the differences in risk catagories of each structure classification. Each type of structure is built to meet distinct needs, often varying greatly in terms of engineering, materials, and regulatory standards. Here’s what you need to know about the differences between ag/ utility structures and res structures, as well as what to consider if you plan on converting an ag or utility structure to residential use in the future.

“Risk Category” is a classification system written in the International Building Code (IBC) that defines the level of risk associated with a structure’s failure. These categories influence design requirements to ensure structures can withstand various hazards like earthquakes, wind, snow, and more, depending on the contents of the building.

There are four levels of risk catagories, beginning with the lowest risk, Risk Category I (RCI) up to the highest risk, Risk Category IV (RCIV.)

In this article we’ll be speaking specifically to RCI and RCII and how they impact barn or barn apartment projects.

Risk category and building code requirements

The most significant difference between agricultural and residential structures is their risk category classification:

Risk category I (RCI): Ag or utility buildings are designed with no living space, minimal utilities and minimal insulation. Ag and utility buildings such as your horse barn, workshop or storage building fall under this category, which means they have lower engineering standards because they pose a minimal threat to human life, as they are not meant to house humans for long periods of time. These structures are typically simpler to build, less costly, and subject to fewer regulatory requirements.

Risk category II (RC2): Res buildings are designed to protect human life from elements like earthquakes, snow and wind, and include living spaces finished with utilities and insulation. Res buildings like barn homes and barn apartments are designed under RCII to ensure greater safety, stability, and durability, meeting higher standards for seismic, wind, and snow loads. These structures prioritize occupant safety, which makes them more expensive to design and build.

RCI and RCII structural and material differences

Foundation Differences and Post Materials: Barn Pros residential models (RCII) use Douglas Fir interior posts, which are more aesthetically pleasing and better to finish for res spaces. Doug Fir select posts are anchored to a slab-on-grade foundation with perimeter 2×6 shear walls providing lateral stability to the structure.

In contrast, Barn Pros agricultural and utility structures (RCI) use pressure-treated (PT) posts that are buried in the ground and encased in concrete. These posts support the structure and siding is mounted directly to the exterior of the posts to create the barn wall. PT posts are durable and less expensive than Doug Fir posts, but not as aesthetically pleasing.

Loft Floor Framing: Residential structures have loft floor framing designed to accommodate utilities within, while also creating necessary space for fire egress dimensions in the loft windows above. Loft heights are carefully calculated to avoid interference with doors and provide functional headspace.

Wall Construction: Residential models are designed with perimeter stud walls that accommodate HVAC, plumbing, electrical systems, and insulation. These walls allows for upgrades such as continuous exterior foam insulation and flame block sheathing for high fire regions. These also accounts for geographic conditions like high water tables, bedrock, and high seismic, snow, or wind loads.

Ag and utility buildings are typically single-wall construction, leaving minimal space for insulation and usually requiring utility runs to be made via exposed conduit. Single-wall construction requires less material and will often costs less, but does not provide as much lateral support to the building, or the higher level of finish standards that stud walls do.

Fire Protection: Residential buildings must meet fire code requirements, ensuring safe window egress and a separation of living space from non-living space via fire code material like drywall. Ag structures aren’t held to these standards, so design, material and construction costs are often lower.

To learn more about how Barn Pros RCI and RCII model designs leverage post-frame construction style, explore the article here: Understanding Post Frame Structure Construction.

Conversions: Re-engineering and re-permitting.

To convert a RCI ag building into a RCII residential space, even if just for part of the building, you will be required to have a third-party engineering firm re-engineer your blue prints to include all necessary RCII building code standards for your area and then you will need to re-permit your structure.  Updating walls, egress window space and creating room for utilities and insulation in your existing structure can require significant renovations, and permitting times can be lengthy and expensive.

If you think RCII may be in your future, design and plan for residential from the beginning.

Because of the additional costs and timelines for engineering, permitting, renovations and materials, Barn Pros recommends planning your project and designing your structure to RCII standards from the beginning, even if you don’t anticipate finishing the space for months or years. This provides you the flexibility to frame your barn and use it as an ag or utility structure for as long as you like, and when the time comes to finish the living space, you already have the permitting and engineering taken care of and your contractor can continue with your project.

Conclusion

The main differences between an agricultural and residential barn boils down to the intended use and the risk case associated with it. Agricultural builds are perfect for barns, workshops, and storage spaces, offering cost savings with fewer design, permitting and material requirements. However, if you have any plans to use the space for living, opting for a barn designed for residential use from the outset could save you from substantial expenses and longer project timelines in the future.